Huaping Zhong

Relationships between altitudinal gradient and plant carbon isotope composition of grassland communities on the Qinghai-Tibet Plateau, China

Foliar and root carbon isotope composition (δ13C) of grassland communities on the Qinghai-Tibet Plateau, China, was obtained by the biomass weighting method and direct measurement. We investigated the characteristics and altitudinal patterns of foliar and root δ13C and determined which environmental factors influenced foliar δ13C most. Foliar δ13C of alpine steppe was significantly higher than that of alpine meadow and temperate steppe. For alpine meadow, root δ13C was significantly higher than of foliar δ13C. Foliar δ13C increased with altitude at an average rate of 0.60‰ km−1 for the whole grassland ecosystem. This rate was lower than that at species level. However, there were no significant relationships between root δ13C and altitude. Atmospheric pressure was a more important factor than temperature and precipitation in its influence on the altitudinal pattern of foliar δ13C at the community level.

Relationships between C3 Plant Foliar Carbon Isotope Composition and Element Contents of Grassland Species at High Altitudes on the Qinghai-Tibet Plateau, China

Relationships of foliar carbon isotope composition (δ13C) with foliar C, N, P, K, Ca, Mg contents and their ratios of 219 C3 species leaf samples, obtained in August in 2004 to 2007 from 82 high altitude grassland sites on the Qinghai-Tibet Plateau China, were examined. This was done with reference to the proposition that foliar δ13C increases with altitude and separately for the life-form groups of graminoids, forbs and shrubs and for the genera Stipa and Kobresia. For all samples, foliar δ13C was negatively related to foliar K, P and ∑K+ Ca+ Mg, and positively correlated to foliar C, C/N and C/P. The significance of these correlations differed for the taxonomic and life-form groups. Lack of a relationship of foliar δ13C with foliar N was inconsistent with the majority of studies that have shown foliar δ13C to be positively related to foliar N due to a decrease of Ci/Ca (the ratio between intercellular and atmospheric concentration of CO2) and explained as a result of greater photosynthetic capacity at higher foliar N concentration. However this inconsistency relates to other high altitude studies that have found that photosynthetic capacity remains constant as foliar N increases. After accounting for the altitudinal relationship with foliar δ13C, of the elements only the K effect was significant and was most strongly expressed for Kobresia. It is concluded that factors critical to plant survival and growth at very high altitudes, such as low atmospheric pressure and low temperatures, may preclude expression of relationships between foliar δ13C and foliar elements that have been observed at lower altitudes.

Patterns of Soil 15N and Total N and Their Relationships with Environmental Factors on the Qinghai-Tibetan Plateau

The patterns of soil nitrogen (N) isotope composition at large spatial and temporal scales and their relationships to environmental factors illustrate N cycle and sources of N, and are integrative indicators of the terrestrial N cycle and its response to global change. The objectives of this study were: i) to investigate the patterns of soil N content and natural abundance of N-15 (delta N-15) values in different ecosystem types and soil profiles on the Qinghai-Tibetan Plateau; ii) to examine the effects of climatic factors and soil characteristics on the patterns of soil N content and soil delta N-15 values; and iii) to test the relationship between soil delta N-15 values and soil C/N ratios across ecosystems and soil profiles. Soil profiles were sampled at 51 sites along two transects 1 875 km in length and 200 km apart and distributed in forest, meadow and steppe on the Qinghai-Tibetan Plateau. Each site was sampled every 10 cm from a soil depth of 0 to 40 cm and each sample was analyzed for soil N content and delta N-15 values. Our results indicated that soil N and delta N-15 values (0-40 cm) in meadows were much higher than in desert steppe. Soil N decreased with soil depth for each ecosystem, while variations of soil delta N-15 values along soil profiles were not statistically significant among most ecosystems but for mountain meadow, lowland meadow, and temperate steppe where soil delta N-15 values tended to increase with soil depth. The parabolic relationship between soil delta N-15 values and mean annual precipitation indicated that soil delta N-15 values increased with increasing precipitation in desert steppe up to 500 mm, and then decreased with increasing precipitation across all other ecosystems. Moreover, the parabolic relationship between delta N-15 values and mean annual temperature existed in all individual ecosystem types. Soil N and delta N-15 values (0-40 cm) increased with an increase in soil silt and clay contents. Furthermore, a threshold of C/N ratio of about 11 divided the parabolic relationship between soil delta N-15 values and soil C/N ratios into positive (C/N 11) parts, which was valid across all ecosystems and soil profiles. The large explanatory power of soil C/N ratios for soil delta N-15 values suggested that C and N concentrations, being strongly controlled by precipitation and temperature, were the primary factors determining patterns of soil delta N-15 on the Qinghai-Tibetan Plateau.

Effects of cutting at different reproductive development stages on aftermath growth of red clover (Trifolium pratense) in a subtropical montane environment

Abstract The use of red clover (Trifolium pratense) in subtropical montane areas of southern China is reviewed as a preliminary to an investigation, at Hongchiba, Wuxi County, Chongquing, of the effects on aftermath growth of cutting at different stages of reproductive development of a local cultivar ‘Wuxi’ red clover. The reproductive stages were branching, flower bud formation, flowering, and seed pod formation. The time taken to reach the defined reproductive stages after cutting, and the height of herbage and yield at cutting, became less with successive cuts. The greatest rate of dry matter accumulation was during the branching and flower bud formation stages. Cutting at the flower bud stage produced the highest total yield of 13 380 kg DM ha−1 and cutting at the pod stage the least yield of 10 480 kg DM ha−1. It is recommended that the first cut should be made about 70 days after the start of spring growth, and the second, third, and fourth harvests 50, 30, and 35 days after the previous harvests.

Adaptive characteristics of grassland community structure and leaf traits along an altitudinal gradient on a subtropical mountain in Chongqing, China

Community structure and leaf traits are important elements of terrestrial ecosystems. Changes of community structure and leaf traits are of particular use in the study of the influence of climate change on terrestrial ecosystems. Patterns of community structure (including species richness, above- and below-ground biomass) and leaf traits (including leaf mass per area (LMA), nitrogen content both on mass and area bases (Nmass and Narea), and foliar δ13C) from 19 grassland plots along an altitudinal transect at Hongchiba in Chongqing, China, were analyzed. Species richness along the altitudinal transect had a hump-shaped pattern. Above-ground biomass had a quadratic decrease along the altitudinal gradient whereas below-ground biomass had the opposite pattern. Change of above-ground biomass of various taxonomic groups with altitude was also studied. Poaceae showed strong negative relationships and Asteraceae showed a hump-shaped relationship with increase of altitude. Five common species of the grassland, Trifolium pratense, Geranium wilfordii,Aster tataricus, Leontopodium leontopodioides, and Spiraea prunifolia, were particularly studied for variation of leaf traits along the altitudinal gradient. Averaged for all species, LMA, Narea and foliar δ13C had positive correlations with altitude. Nmass did not change significantly as altitude increased. LMA and Narea showed significant positive relationships with foliar δ13C. The adaptive features of leaf traits among different species were not consistent. The study highlights specific adaptation patterns in relation to altitude for different plant species, provides further insights into adaptive trends of community structure and leaf traits in a specific ecological region filling a gap in the definition of global patterns, and adds to the understanding of how adaptive patterns of plants may respond to global climate change.